weston-ini-conf: add virtio-aarch64 configuration

weston-ini-conf: add virtio-aarch64 configuration

Add a WESTON_DISPLAYS tweak for the virtio-aarch64 machine so the
demo platform image gets the required weston configuration when
built for it.

Bug-AGL: SPEC-4618

Change-Id: I90974a25d51fc3b4ad3d8e9450d98f8ae82f759a
Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/28187
Tested-by: Jenkins Job builder account
ci-image-build: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
(cherry picked from commit 50a5f20e1dfe4f9fb6b8ba8dec865e2f8cdaf09f)
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/28279